Myocardial ischemia and subsequent heart failure are leading causes of hospitalization and death. Stem cells are a promising treatment modality for injured cardiac tissue and may mediate their beneficial cardiac effects in part by paracrine mechanisms. Stem cell treatment of injured cardiac tissue may reduce inflammation, apoptosis, infarct size and improve function via factors that promote tissue repair. This paracrine protection may be enhanced by ex vivo modification. Genetic modification, VEGF transduction, and even preconditioning have been shown to enhance stem cell paracrine cardioprotection in animal models. Interestingly, we have recently shown that modulation of cytokines may enhance protective growth factor production. IL-18, a novel member of the IL-1 cytokine superfamily, is now recognized as an important regulator of innate and acquired immune responses. Recent research indicates that IL-18 may play an important role in acute graft versus host disease after stem cell transplantation. IL-18 has also been reported to play an antiangiogenic role in bone marrow derived endothelial progenitor cells. However, the effect of IL-18 on bone marrow mesenchymal stem cell (MSC) production of growth factors remains unknown. Thus, it is important to delineate the effects of IL-18 signaling in stem cell activation in order to further understand the role of stem cells in cardiac disease and maximize stem cell protective factors during therapeutic myocardial protection. We hypothesize that: 1) IL-18 will decrease MSC production of growth factors through p38 MARK, ERK or Akt signals;2) IL-18 binding protein may neutralize the negative effects of IL-18 on MSC release of growth factors and enhance MSC cardioprotection during ischemia and reperfusion (I/R). To address these hypotheses we propose the following four specific aims: 1. To determine whether IL-18 signaling affects activated mesenchymal stem cell production of VEGF, HGF, IGF-1 and the cytokine TNF, and if so, whether this effect is mediated by p38 MARK, ERK, or Akt signaling. 2. To determine whether IL-18 binding protein may neutralize the effect of IL-18 on MSC release of VEGF, HGF, IGF-1 and the cytokine TNF. 3. To elucidate whether IL-18 signaling affects mesenchymal stem cell proliferation and apoptosis, and if so, whether targeted knockdown of VEGF or HGF expression by siRNA may neutralize these effects. 4. To determine whether MSC myocardial protection during I/R may be enhanced by IL-18 binding protein. PUBLIC HEALTH IN LAY TERMS: Bone marrow stem cells may be useful to fix injured hearts. We aim to study a protein called IL-18 so that we can utilize the ability of stem cells to protect the heart.